1. Field Of the Invention
The present invention relates generally to a method and apparatus for counting flat sheets of specularly reflective material and, more specifically, to a method and apparatus for sensing and counting flat sheets of glass.
2. Description Of the Related Art
Specularly reflective material such as glass is manufactured for many commercial, residential and automotive applications. Glass is commonly manufactured in the form of a substantially flat or planar sheet. Planar sheets of glass are manufactured in many sizes having different thicknesses and characteristics to match the requirements of the intended application. Each planar sheet of glass is typically cut from a larger sheet of glass. When a smaller sheet of glass is cut from a larger sheet of glass, the larger sheet is scribed to form a line of cut and then essentially broken along the line of cut. A cut side of the planar sheet of glass is generally smooth except at an edge adjacent the line of cut which, relatively speaking, is rough. When collimated light is shined on the cut side of the planar sheet of glass, the light will be specularly reflected except at this rough edge where it is substantially diffusely reflected.
Once the planar sheet of glass is cut to size, similar sheets of glass having various thicknesses may be packaged such that they are tightly juxtaposed in side by side relationship with respect to one another, crated and shipped. Once the sheets of glass are crated, the quantity or number of sheets of glass in each crate must be determined. One way to determine this is to have the sheets of glass manually counted. Unfortunately, human error being what it is, the number of sheets of glass is often miscounted, causing returns of surplus sheets of glass and deficiencies in the number of sheets of glass.
One effort to overcome miscounting is disclosed in U.S. Pat. No. 4,298,790 issued to Decker et al. on Nov. 3, 1981 for a Method And Apparatus For Determining The Number Of Sheets In A Stack. This patented apparatus discloses a scanner including a sensor for sensing the edge of the outer most stacked sheets and the interface between adjacent sheets. The patented apparatus also discloses a source or emitter for directing infrared light toward the sides of the stacked sheets and a detector for sensing the density of the specularly reflected infrared energy rays. The reflected infrared energy rays are a maximum density when reflected from a plane generally parallel to the surface of the emitter and detector and the density decreases when the rays are incident on the edges of the outermost stacked sheets and on the interface between adjacent stacked sheets. The patented apparatus measures the density of the specularly reflected light and a sheet is counted when the light density drops below a predetermined value, as for example, when light is diffusely reflected at the edges of the sheet, in this case, glass.
Due to unwanted "noise" and specular reflection at the edge of a sheet of glass, the patented apparatus suffers from the disadvantage that it is often difficult to determine whether the light density has indeed decreased sufficiently for a count to be made. Inaccuracies in counts can often occur necessitating further attempts to scan the edges and perform manual counts for further accuracy.